Sparkgap assembly having horngap end electrodes

ABSTRACT

A sparkgap assembly for a surge voltage arrester is provided with a plurality of elongated electrodes mounted between stacked plates of insulating material to form a zigzag discharge path through the sparkgap assembly when it is sparked over. The sparkgap assembly is provided with uniquely formed end plates that provide corona shielding and contact the outer electrodes of the assembly in a manner such that these electrodes develop an arc-moving, horngap effect when an overvoltage surge is discharged through the assembly.

United States Patent [72] inventors Earl W. Stetson Pittsfield; Francis J. Charewicz, Lanesboro, both of Mass.

[21] Appl. No. 886,102

[22] Filed Dec. 18, 1969 [45] Patented Oct. 19, 1971 [73] Assignee General Electric Company [54] SPARKGAP ASSEMDLY HAVING HORNGAP END ELECTRODES 16 Claims, 9 Drawing Figs.

[52] US. Cl 315/36 [51] Int. Cl "0115/00, H02h 9/06 [50] Field of Search 315/36 Primary Examiner-Roy Lake Assistant ExaminerDarwin Rt Hostetter Attorneys-Francis X. Doyle, Vale P. Myles, Frank L Neuhauser, Oscar B. Waddell and Joseph B. Forman ABSTRACT: A sparkgap assembly for a surge voltage arrester is provided with a plurality of elongated electrodes mounted between stacked plates of insulating material to form a zigzag discharge path through the sparkgap assembly when it is sparked over. The sparkgap assembly is provided with uniquely formed end plates that provide corona shielding and contact the outer electrodes of the assembly in a manner such that these electrodes develop an arc-moving, horngap effect when an overvoltage surge is discharged through the assembly.

SPARKGAP ASSEMBLY HAVING IIORNGAP END ELECTRODES In the lightning arrester field, it is a well recognized fact that by properly controlling the movement of the discharge and power follow currents through a lightning arrester sparkgap assembly it is possible to utilize the magnetic fields generated by the follow current to stretch the arcs formed in the gaps of the assembly so that the arrester is quickly cleared and resealed following a discharge operation. Infact, this homgap effect has been successfully utilized in the design and manufacture of relatively inexpensive distribution lightning arresters of a type disclosed and claimed in one of an earlier filed US. Pat. application, Ser. No. 736,770-Stetson, filed June 13, I968, and assigned to the assignee of the present invention. In arresters of this type, the size of the sparkgap assembly is ordinarily determined by two factors; namely, the spark over voltage rating of the arrester and its clearing and rescaling ability. The first of these factors is controlled primarily by the number and size of sparkgaps in the arresters sparkgap assembly; whereas, the second factor is controlled by the combined operation of the electromagnetic arcstretching ability of the arrester and the current-limiting effect of one or more nonlinear resistances connected in series with the sparkgap assembly.

From the foregoing remarks, it is apparent that in order to improve the clearing and rescaling capabilities of a lightning arrester it is necessary toeither increase the amount of nonlinear resistance valve material electrically connected in series with the arresters sparkgap assembly or, alternatively, to increase the elcctrodynamic arch-stretching ability of the spark gap assembly to rapidly deionize the arc and increase the reseal ability of the arrester. In the highly competitive commercial atmosphere now prevailing in lighting arrester markets, the first of these expedients is not economically practical. Accordingly, numerous attempts have been made in the prior art to develop sparkgap assemblies having improved arcstretching capabilities. Relatively recent examples of such efforts are disclosed in US. Pat. No. 3,069,589Cunningham and No. 3,152,279-Misare, as well as the improvement disclosed and claimed in the above-identified Stetson application. The invention disclosed and claimed herein is a further improvement over these various prior art patents relating to means for increasing the electromagnetic arc-driving characteristics of a sparkgap assembly.

In one preferred form of the invention, a sparkgap assembly is fonned by mounting one or more electrodes between a plurality of stacked insulating plate members that have a pair of elongated terminal members respectively mounted on the opposite ends of the stacked assembly. Pursuant to the unique characteristics of our invention, a corona shield terminal plate is mounted over each end of the stacked assembly in a manner such that electrical contact is made only with the respective ends of the elongated terminals remote from their respective sparkgaps. This unique construction forces a follow current passing through the sparkgap assembly to follow a sinuous path that produces a strong arc-moving homgap effect at each of the assemblys sparkgaps, rather than simply having such a homgap effect developed at intermediate sparkgaps of the assembly, as was uniformly the practice with prior art arresters of the type described in the above reference patents.

A primary object of our invention is to provide a sparkgap assembly that is more economical to manufacture than prior art sparkgap assembly structures and that has improved electromagnetic arch driving operating characteristics.

Another object of our invention is to provide an inexpensive, simplified sparkgap assembly having a plurality of sparkgaps, each of which are integrall formed with arc-driving homgaps that are operative to electromagnetically drive arcs outward therefrom when an overvoltage surge is discharged through the assembly.

A further object of the invention is to provide a sparkgap assembly having a combination corona shield and end sparkgap terminal.

Further objects and advantages of the invention will become apparent from the following description taken in conjunction with the attached drawings in which:

FIG. 1 is an exploded perspective view of a sparkgap assembly for a surge voltage arrester constructed pursuant to the invention disclosed herein.

FIG. 2 is a perspective view of the sparkgap assembly shown in FIG. 1, depicting the component parts of this assembly in operative relationship in combination with a nonlinear valve member.

FIG. 3 is a side elevation, cross-sectional view of the sparkgap assembly and nonlinear valve arrangement illustrated in FIG. 2.

FIG. 4 is a schematic circuit diagram of one type of prior art lightning arrester.

FIG. 5 is a schematic circuit diagram of a lightning arrester similar to that illustrated in FIG. 2.

FIG. 6 is a top plan view of an alternative embodiment of an end plate terminal for a sparkgap assembly constructed pursuant to our invention.

FIG. 7 is a side elevation view, in cross section, along the plane 77 of the terminal plate illustrated in FIG. 6

FIG. 8 is an exploded perspective view of yet another embodiment of our invention illustrating one type of elongated terminal and terminal plate for a sparkgap assembly constructed pursuant to the invention.

FIG. 9 is a perspective view of the component parts of the embodiment of the invention illustrated in FIG 8, showing the parts in assembled position.

Referring now to FIGS. 1 and 2 of the drawing, there is shown the separate component parts of a sparkgap assembly I of a type that is suitable for use with a block of nonlinear resistance valve material 2 to form a low-voltage distribution surge voltage arrester. As seen in FIG. I, sparkgap assembly I comprises a plurality of insulating plate members 3 and 4 having apertures 5 and 6, respectively, formed therethrough; a pair of elongated end terminals 7 and 8; an elongated intermediate terminal 9 and a pair of terminal plates 10 and II. In the preferred form of our invention, the insulating plates 3 and 4 are made of a suitable insulating material and the elongated terminals 7 and 8 and electrode 9 may be formed of a suitable copper-base alloy having relatively good conductance as is well known in the lightning arrester art. Terminal plates I0 and 11 are formed of an iron-base alloy that is relatively inexpensive compared with other conducting alloys, while at the same time being suitably conductive to afford adequate corona shielding for the respective ends of the stacked components of sparkgap assembly I.

It will be understood by those skilled in the art that the rating of sparkgap assembly 1 can be increased by increasing the number of insulating plates and associated elongated electrodes, such as electrode 9, that are stacked within a given assembly, thereby to increase the number of sparkgaps in the assembly. However, in order to emphasize the desirable features of our invention, a minimum number of elongated electrodes; namely one, i.e., electrode 9, is illustrated in the embodiment of the invention depicted in FIG. I It will also be understood that electrode 9 and all similar electrodes that may be used in other embodiments of the invention, are identical and each comprise a generally flat body portion 12 and a pair of integral abutments l3 and 14 that protrude, respectively, from opposite sides of each of the body portions 12. Moreover, each of these elongated electrodes 9 (etc.) are provided with means for positioning them in relatively fixed position between a pair of insulating plate members, such as plate members 3 and 4, so that their abutments (I3 and I4) extend partially into one of the apertures (5 and 6) in such sandwiching plate members. In the embodiment of the invention shown, these positioning means comprise two pair of tabs, 15-15:: and 16-- 16a on op posite ends of elongated electrode 9, and cooperating detents I5, I50 and I6, 16a in the respective bottom and top surfaces of insulating plate members 3 and 4. as shown in FIG. I. When the sparkgap assembly components are stacked as shown in FIG. 2, the positioning means l5-l6a' position elongated electrode 9 so that integral abutment 13 extends partially into aperture 5 and integral abutment 14 extends partially into aperture 6 in insulating plate 4.

In a similar manner, the respective elongated terminals 7 and 8 each comprise a generally flat body portion 7a and 80, respectively, having abutments 7b and 8b protruding therefrom. Tabs 17 and 17a on elongated terminal 7 cooperate with detents l7 and 17a on the top surface of insulating plate 3 and tabs 18 and 18a on elongated terminal 8 cooperate with detents l8 and 180' on the bottom surface of insulating plate member 4 to support these elongated terminals 7 and 8 in operating position adjacent these outer end surfaces of sparkgap assembly 1 so that the protruding abutments 7b and 8b extend, respectively, partially into apertures 5 and 6 thereby to form sparkgaps with abutments l3 and 14 on elongated electrode 9. These two sparkgaps 7-9 and 9-8 are perhaps best seen in the cross-sectional view shown in FIG. 3 of the drawings.

As seen in FIGS. 1, 2 and 3, the terminal plates 10 and 11 are generally Ushaped and have their respective base portions 10a and 11a in electrical contact with the ends of elongated terminals 7 and 8 adjacent the ends thereof remote from the sparkgaps formed by abutment 7b and 8b. As is seen in FIG. 2, the respective legs 10b and 10c of terminal plate 10 are positioned substantially parallel to the longitudinal axis of elongated terminal 7 and it will be understood that the respective legs of terminal plate I 1 are similarly generally parallel to the longitudinal axis of elongated terminal 8 when the components of sparkgap assembly 1 are in operative position. In this embodiment of the invention, the legs of each of the U- shaped terminal plates 10 and 11 are mounted in substantially the same plane as that occupied by the generally flat portions 7a and 8a of the elongated terminals 7 or 8 that are electrically connected to the base portion thereof. Thus, as can best be seen in FIG. 2, the upper surface of insulating plate member 3 supports substantially the entire surface area of the legs 10b and 100 of terminal plate 10 and also supports the generally flat portion 7a of elongated terminal 7.

In order to stabilize the stacking arrangement of assembly 1, terminal plates 10 and 11 are also provided with additional raised portions 10d, 10c and 11d, 1 1e, respectively, the uppermost surfaces of which lie in the same planes as the uppermost surfaces of raised portions 100 and Ila, respectively, so that additional sparkgap assemblies or nonlinear valve blocks can be stacked on top of sparkgap assembly 1 if desired. In order to insure good resilient contact between the elongated terminals 7 and 8, the respective raised portions 100 and 11a of terminal plates 10 and 11 are formed to define channels that are at least 2 mils shallower than the thickness of the elongated terminals 7 and 8 so that when these component parts are in assembled position on top of the outer surfaces of insulating plates 3 and 4, as shown in FIG. 2, good electrical contact is formed by the mechanical contact between these electrodes and terminal plates.

In order to hold the terminal plates 10 and 11 in a desired position on the ends of sparkgap assembly 1, holding means comprising a pair of apertures 19 and 19a in terminal plate 10 and 20 and 20a in terminal plate 11 are formed to fit, respectively, around abutments 19' and 19a on the top surface ofinsulating plate member 3 and abutments 20' and 20a on the bottom surface of insulating plate member 4. It will be apparent that a single aperture in each terminal plate would suffice to hold terminal plates 10 and 11 in position because of the interlocking effect on these terminal plates between raised channels 10a and 11a and elongated terminals 7 and 8, respectively.

In the operation of a surge voltage arrester constructed pursuant to the embodiment of our invention depicted in FIGS. 1, 2 and 3, an arc discharge current will be forced to follow a sinuous path from uppermost terminal plate 10 to lower terminal plate 11 and thence through nonlinear valve 2 to ground. This sinuous path is shown generally by the dotted line 21 illustrated in FIG. 3. Accordingly, both of the sparkgaps formed by cooperating elongated terminals 7 and 8 and intennediate electrode 9 produce a strong arc-moving electromagnetic horngap effect that drives the arcs formed in all of these sparkgaps outward therefrom to quickly extinguish the arcs and thus reseal the arrester.

Referring to FIGS. 4 and 5 of the drawing, it can be seen that the type of horngap effect produced by the arrester embodiment of the invention depicted in FIGS. 1-3 is schematically represented by the circuit shown in FIG. 5 in which a protected conductor 22 is connected through a pair of horngaps 7-9 and 9-8 and a nonlinear valve resistance 2 to ground. I-Iorngaps 7-9 and 9-8 correspond to the homgapped sparkgaps illustrated in FIG. 3. FIG. 4 of the drawing illustrates the type of sparkgap that would normally result from the use of prior art lightning arrester end terminal sparkgap structures if only one intermediate electrode and two end terminals were utilized, because the end terminal plates of such arresters normally short out any possible horngap effect and thereby reduce the end sparkgaps of the assembly to simple, nonarc moving or stretching sparkgaps. Thus, the discharge circuit would be from a protected conductor 22' through a pair of nonarc-moving sparkgaps 23 and 24 thence through a nonlinear valve resistance 25 to ground. Consequently, in such arrangements the nonlinear resistance valve 25 would have to be much larger than the nonlinear resistance valve 2 shown in the circuit of FIG. 5 in order to cause the protective surge voltage arresting circuit to clear at an equivalent voltage rating. Alternatively, additional gaps could be inserted in the circuit of FIG. 4 to achieve the current reseal ability, afforded by the two gaps illustrated in the circuit of FIG. 5, which is representative of the type of economical and improved sparkgap as sembly that can be constructed pursuant to the teachings of our invention, as described above with reference to FIGS. 1-3 of the drawings.

Now that the basic structure and principles of operation of one embodiment of our invention have been described. reference is made to FIGS. 6 and 7 of the drawings in which there is depicted an alternative embodiment of a terminal plate 26 comprising a base portion 26a and three integral legs, 26b, 26c and 26d extending substantially in parallel from one side thereof. The center leg 26c has an abutment 27 formed therein to afford a sparkgap contact that performs the same function as abutment 7b on elongated electrode 7 of the embodiment of our invention depicted in FIGS. 1-3. Thus, it can be seen that with this embodiment of our invention, a single terminal plate member 26 replaces the two-part elongated terminal 7 and terminal plate 10 of the embodiment of the invention depicted in FIGS. 1-3. Of course, a similar one-piece terminal plate can also be used to replace the terminal plate 11 and elongated terminal 8 on the bottom of a sparkgap assembly similar to sparkgap assembly I, if desired. At this point, it should be understood that it is not necessary to utilize the horngap forming end electrode structure of our invention at both ends of a sparkgap assembly, such as sparkgap assembly 1, although such an expedient will ordinarily be used to obtain a maximum clearing rating with a minimum number of intermediate sparkgaps being required. Of course, by eliminating the horngap effect at one end of the sparkgap assembly l, the rescaling voltage rating of the assembly would be somewhat lowered if all other characteristics of the as sembly remained constant. The other pertinent structural features of the terminal plate 26 shown in FIG. 6 are a pair of elongated raised channels 28 and 29 therein, substantially parallel to the central leg 26c to stabilize the stacking arrangement of the sparkgap assembly on which terminal plate 26 will be mounted, in the manner discussed above with reference to raised portions 10d, 10c and Ild, 11: on tenninal plates 10 and 11 respectively. These raised channels 28 and 29 also form electrical contacts that can complete a circuit to another sparkgap assembly, or to other suitable electric terminal means mounted thereon or in contact therewith. Also, a pair of apertures 30 and 31 are provided in terminal plate 26 to afford holding means analogous to the apertures 19 and 19a in terminal plate 10. The operation of a terminal plate constructed pursuant to the teachings of FIG. 6 and 7 would be similar to the operation described above with reference to the embodiment of the invention depicted in FIGS. 1 and 3, assuming such a plate is mounted on a sparkgap assembly such as assembly 1, in lieu of plate and terminal 7 thereof.

Another embodiment of our invention is illustrated in FIGS. 8 and 9, FIG. 9 being an assembled view and FIG. 8 being an exploded view of the same structure. This structure is quite similar to that described above with reference to FIGS. ll3 and it will be understood that the component parts are assembled in an analogous manner and operate in substantially the same manner as those parts described above. Thus, an end insulating plate member 32 having an aperture 33 therein is provided with a pair of abutments 34 and 35 that cooperate with apertures 36 and 37, respectively, in a flat terminal plate 39, that overlies an outer end of elongated electrode 40 remote from an abutment 41 thereon that, inassembled position, extends partially into aperture 33 to form a sparkgap with a cooperating intermediate electrode (not shown), in the manner discussed above with reference to the embodiment of the invention illustrated in FIGS. 1-3. Elongated electrode 40 has a tab 42 at its outer end that is positioned in detent 43 in insulating plate 32 to hold the electrode in operating position when the component parts of the assembly are in operating position. It will be appreciated that with this embodiment of our invention the mechanical stacking stability of a sparkgap assembly incorporating plate 39 is extremely good because the outer surface of plate 39 is substantially flat and thus affords a stable support surface on which to mount additional assemblies or series connected valve blocks. As will be appreciated by those skilled in the art from the description of the embodiment of our invention shown in FIGS. 1-3, the channel 44 formed in insulating plate 32 to accommodate elongated terminal 40 should be at least 2 mils shallower than the thickness of elongated terminal 40 so that good electrical contact is assured between terminal 40 and the base portion of terminal plate 39. Otherwise, additional electrical contact forming means between these two members must be provided.

It will be apparent from the foregoing description of our invention that various modifications and improvements may be made therein and it is intended to encompass all alternative forms of the invention within the true scope and spirit of the appended claims.

What we claim as new. and desire to secure by Letters Patent of The United States is:

l. A sparkgap assembly comprising a plurality of stacked insulating plate members, means defining an aperture through each of said plate members, a number of elongated electrodes, each of said electrodes comprising a generally fiat body portion and a pair of integral abutments protruding respectively from opposite sides of said body portion, means supporting each of said electrodes in relatively fixed position between a pair of said plate members with each of the abutments of the electrodes extending partially into one of said apertures, a pair of elongated terminals, each of said terminals comprising a generally flat body portion and an integral abutment protruding from one side of said body portion, means supporting each of said terminals in relatively fixed position adjacent the respective outer ends of said stack of plate members with the abutment of each terminal extending partially into the apertures through the outer plate members to form spark gaps in said apertures with the abutments on said electrodes that also extend partially into said apertures, a pair of terminal plates respectively mounted over a portion of said elongated terminals adjacent the ends thereof most distant from the abutments protruding from said terminals, means forming an electrical connection between said terminal p ates and said elongated terminals adjacent said respective ends thereof most distant from the abutments protruding therefrom whereby said elongated terminals cooperate with the elongated electrode next adjacent them in the stack of insulating plate members to produce an arc-driving magnetic field when an arc is formed across the sparkgaps of said sparkgap assembly, said arc-driving magnetic field being effective to drive arcs out-- ward from the sparkgaps formed between the elongated terminals and the elongated electrodes adjacent said terminals.

2. A sparkgap assembly as defined in claim 1 wherein said terminal plates are generally U-shaped, the respective base portions of said U-shaped plates being electrically connected to said elongated terminals, and the legs of said U-shaped plates being positioned substantially parallel to the longitudinal axes of said elongated terminals.

3. A sparkgap assembly as defined in claim 2 wherein the legs of each of said U-shaped terminals are mounted in substantially the same plane as that occupied by the generally fiat portion of the elongated terminal that is electrically connected to the base portion thereof.

4. A sparkgap assembly as defined in claim 3 wherein part of the base portions of said U-shaped terminals are raised thereby to define a channel with respect to the legs thereof, said channel being at least 2 mils shallower than the thickness of said elongated plates electrically connected thereto so that a resilient contact is formed between the base portion of the terminal plate and the elongated plates under it when said plates and the legs of said plate are supported in a common plane on the surface of one of said stacked insulating plate members.

5. A sparkgap assembly as defined in claim 4 wherein each of the legs of said U-shaped terminal plates include a raised portion the respective upper surfaces of which are in a common plane with the upper surface of the raised portion on the respective bases of said U-shaped terminal plates.

6. A sparkgap assembly as defined in claim 2 wherein at least one of said terminal plates is generally flat so that its base portion and legs are positioned in a common plane, and including means defining a channel in the end insulating plate member under said one of said terminal plates, said channel being adapted to receive the elongated terminal in contact with said one of said terminal plates therein, whereby the legs of said terminal plate are supported over substantially their entire extent by the surface of said end insulating plate member and part of the base portion of the terminal plate is supported at its point of contact by said elongated terminal.

7. A sparkgap assembly as in claim 2 wherein said elongated terminals are formed of a copper alloy and said terminal plates are formed of an iron alloy.

8. A sparkgap assembly as defined in claim 2 including holding means on at least one leg of each terminal plate for holding said plate in a predetermined position with respect to the end insulating plate member on which it is mounted, and an abutment formed on each of said end insulating plates respectively to cooperate with said holding means to afford said holding function.

9. A sparkgap assembly as defined in claim 8 wherein said holding means comprises means defining an aperture in said at least one leg, said aperture being formed to fit around the abutment on said end plate.

10. A sparkgap assembly as defined in claim I wherein said number of elongated electrodes comprises at least two electrodes.

111. A sparkgap assembly as in claim I wherein said number of elongated electrodes comprises a single electrode.

12. A sparkgap assembly comprising a plurality of stacked insulating plate members, means defining an aperture through each of said plate members, a number of elongated electrodes, each of said electrodes comprising a generally flat body portion and a pair of integral abutments protruding respectively from opposite sides of said body portion, means supporting each of said electrodes in relatively fixed position between a p ir of said plate members with each of the abutments of the electrodes extending partially into one of said apertures, a pair of elongated terminals, each of said terminals comprising a generally fiat body portion and an integral abutment protruding from one side of said body portion, means supporting each of said terminals in relatively fixed position adjacent the respective outer ends of said stack of plate members with the abutment of each terminal extending partially into the apertures through the outer plate members to form sparkgaps in said apertures with the abutments on said electrodes, a terminal plate mounted over a portion of one of said elongated terminals adjacent the end thereof most distant from the abutment protruding therefrom, means forming an electrical connection between said terminal plate and said elongated terminal adjacent said end thereof most distant from the abutment protruding therefrom, whereby said elongated terminal cooperates with said elongated electrode to produce an aredriving magnetic field when an arc is discharged across the sparkgaps of said sparkgap assembly, said arc-driving magnetic field being effective to drive an arc outward from said sparkgap formed between the elongated terminal and the elongated electrode adjacent said electrode plate.

13. A sparkgap assembly comprising a plurality of stacked insulating plate members, means defining an aperture through each of said plate members, a number of elongated electrodes, each of said electrodes comprising a generally flat body portion and a pair of integral abutments protruding respectively from opposite sides of said body portion, means supporting each of said electrodes in relatively fixed position between a pair of said plate members with each of the abutments of the electrodes extending partially into one of said apertures, a pair of terminal plates respectively mounted over the outermost ends of said stacked insulating plate members, each of said terminal plates comprising a generally flat body formed as a base portion having three integral legs extending outward from one side thereof, said legs being spaced apart sufficiently to prevent arcs from being formed between them when the sparkgap assembly is operative to discharge an overvoltage surge between said terminal plates, holding means for holding each of said terminal plates in relatively fixed position with respect to the apertures through the end insulating plate members thereby to form a sparkgap between each of the middle legs of the terminal plates and the respective electrode abutments extending into the apertures in said end insulating plate members.

14. A sparkgap assembly as defined in claim 13 including an abutment on each of said middle legs of said tenninal plates adjacent the ends of said legs remote from the respective base portions of the terminal plates, said abutments being positioned by said holding means to extend into the apertures in the respective end insulating plates to form a sparkgap with the electrode abutments also positioned in said apertures.

15. A sparkgap assembly as defined in claim 14 wherein said holding means comprises means defining at least two spacedapart apertures in each of said terminal plates, and cooperating abutments on the outer surfaces of the end insulating plate members that fit snugly into said apertures to restrict movement between the terminal plates and the insulating plate members, and including a plurality of abutments on said terminal plates the outermost protruding surfaces of which lie in a common plane with the outermost surfaces of the abutments on said insulating plate members when said terminal plates are mounted in operative position in said sparkgap assembly.

16. A sparkgap assembly comprising a plurality of stacked insulating plate members, means defining an aperture through each of said plate members, a number of elongated electrodes, each of said electrodes comprising a generally flat body portion and a pair of integral abutments protruding respectively from opposite sides of said body portion, means supporting each of said electrodes in relatively fixed position between a pair of said plate members with each of the abutments of the electrodes extending partially into one of said apertures, a pair of terminal plate means respectively mounted over the outermost ends of said stacked insulating plate members, each of said terminal plate means comprising three electrically conductive leg portions that are mounted in generally parallel relationship to each other, and means electrically connecting said three leg ortions together adjacent one of the mutuallly juxtaposed en 5 thereof, said legs being spaced apart su lciently to prevent arcs from being formed between them when the sparkgap assembly is operative to discharge an overvoltage surge between said terminal plates, holding means for holding each of said terminal plates in relatively fixed position with respect to the apertures through the end insulating plate members thereby to form a sparkgap between each of the middle legs of the terminal plate means and the respective electrode abutments extending into the apertures in said end insulating plate members.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION P t-m 261M352? Dated October 19. 1971 lnventofls) Earl W. Stetson and Francis J. Char-ewicz It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 1, line 66, "arch" should be arc Col. 6, lines 22, 2 k and 25, "plates" should be terminal-- Col. 7, line 11, after "said" insert one of said "terminal" should be terminals Signed and sealed this 9th day of May 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROERT GO'I'TSCHALK Attesting Officer Commissioner of Patents 

1. A sparkgap assembly comprising a plurality of stacked insulating plate members, means defining an aperture through each of said plate members, a number of elongated electrodes, each of said electrodes comprising a generally flat body portion and a pair of integral abutments protruding respectively from opposite sides of said body portion, means supporting each of said electrodes in relatively fixed position between a pair of said plate members with each of the abutments of the electrodes extending partially into one of said apertures, a pair of elongated terminals, each of said terminals comprising a generally flat body portion and an integral abutment protruding from one side of said body portion, means supporting each of said terminals in relatively fixed position adjacent the respective outer ends of said stack of plate members with the abutment of each terminal extending partially into the apertures through the outer plate members to form spark gaps in said apertures with the abutments on said electrodes that also extend partially into said apertures, a pair of terminal plates respectively mounted over a portion of said elongated terminals adjacent the ends thereof most distant from the abutments protruding from said terminals, means forming an electrical connection between said terminal plates and said elongated terminals adjacent said respective ends thereof most distant from the abutments protruding therefrom whereby said elongated terminals cooperate with the elongated electrode next adjacent them in the stack of insulating plate members to produce an arc-driving magnetic field when an arc is formed across the sparkgaps of said sparkgap assembly, said arcdriving magnetic field being effective to drive arcs outward from the sparkgaps formed between the elongated terminals and the elongated electrodes adjacent said terminals.
 2. A sparkgap assembly as defined in claim 1 wherein said terminal plates are generally U-shaped, the respective base portions of said U-shaped plates being electrically connected to said elongated terminals, and the legs of said U-shaped plates being positioned substantially parallel to the longitudinal axes of said elongated terminals.
 3. A sparkgap assembly as defined in claim 2 wherein the legs of each of said U-shaped terminals are mounted in substantially the same plane as that occupied by the generally flat portion of the elongated terminal that is electrically connected to the base portion thereof.
 4. A sparkgap assembly as defined in claim 3 wherein part of the base portions of said U-shaped terminals are raised thereby to define a channel with respect to the legs thereof, said channel being at least 2 mils shallower than the thickness of said elongated plates electrically connected thereto so that a resilient contact is formed between the base portion of the terminal plate and the elongAted plates under it when said plates and the legs of said plate are supported in a common plane on the surface of one of said stacked insulating plate members.
 5. A sparkgap assembly as defined in claim 4 wherein each of the legs of said U-shaped terminal plates include a raised portion the respective upper surfaces of which are in a common plane with the upper surface of the raised portion on the respective bases of said U-shaped terminal plates.
 6. A sparkgap assembly as defined in claim 2 wherein at least one of said terminal plates is generally flat so that its base portion and legs are positioned in a common plane, and including means defining a channel in the end insulating plate member under said one of said terminal plates, said channel being adapted to receive the elongated terminal in contact with said one of said terminal plates therein, whereby the legs of said terminal plate are supported over substantially their entire extent by the surface of said end insulating plate member and part of the base portion of the terminal plate is supported at its point of contact by said elongated terminal.
 7. A sparkgap assembly as in claim 2 wherein said elongated terminals are formed of a copper alloy and said terminal plates are formed of an iron alloy.
 8. A sparkgap assembly as defined in claim 2 including holding means on at least one leg of each terminal plate for holding said plate in a predetermined position with respect to the end insulating plate member on which it is mounted, and an abutment formed on each of said end insulating plates respectively to cooperate with said holding means to afford said holding function.
 9. A sparkgap assembly as defined in claim 8 wherein said holding means comprises means defining an aperture in said at least one leg, said aperture being formed to fit around the abutment on said end plate.
 10. A sparkgap assembly as defined in claim 1 wherein said number of elongated electrodes comprises at least two electrodes.
 11. A sparkgap assembly as in claim 1 wherein said number of elongated electrodes comprises a single electrode.
 12. A sparkgap assembly comprising a plurality of stacked insulating plate members, means defining an aperture through each of said plate members, a number of elongated electrodes, each of said electrodes comprising a generally flat body portion and a pair of integral abutments protruding respectively from opposite sides of said body portion, means supporting each of said electrodes in relatively fixed position between a pair of said plate members with each of the abutments of the electrodes extending partially into one of said apertures, a pair of elongated terminals, each of said terminals comprising a generally flat body portion and an integral abutment protruding from one side of said body portion, means supporting each of said terminals in relatively fixed position adjacent the respective outer ends of said stack of plate members with the abutment of each terminal extending partially into the apertures through the outer plate members to form sparkgaps in said apertures with the abutments on said electrodes, a terminal plate mounted over a portion of one of said elongated terminals adjacent the end thereof most distant from the abutment protruding therefrom, means forming an electrical connection between said terminal plate and said elongated terminal adjacent said end thereof most distant from the abutment protruding therefrom, whereby said elongated terminal cooperates with said elongated electrode to produce an arc-driving magnetic field when an arc is discharged across the sparkgaps of said sparkgap assembly, said arc-driving magnetic field being effective to drive an arc outward from said sparkgap formed between the elongated terminal and the elongated electrode adjacent said electrode plate.
 13. A sparkgap assembly comprising a plurality of stacked insulating plate members, means defining an aperture through each of said plate members, a number of elongated electrodes, each of said eLectrodes comprising a generally flat body portion and a pair of integral abutments protruding respectively from opposite sides of said body portion, means supporting each of said electrodes in relatively fixed position between a pair of said plate members with each of the abutments of the electrodes extending partially into one of said apertures, a pair of terminal plates respectively mounted over the outermost ends of said stacked insulating plate members, each of said terminal plates comprising a generally flat body formed as a base portion having three integral legs extending outward from one side thereof, said legs being spaced apart sufficiently to prevent arcs from being formed between them when the sparkgap assembly is operative to discharge an overvoltage surge between said terminal plates, holding means for holding each of said terminal plates in relatively fixed position with respect to the apertures through the end insulating plate members thereby to form a sparkgap between each of the middle legs of the terminal plates and the respective electrode abutments extending into the apertures in said end insulating plate members.
 14. A sparkgap assembly as defined in claim 13 including an abutment on each of said middle legs of said terminal plates adjacent the ends of said legs remote from the respective base portions of the terminal plates, said abutments being positioned by said holding means to extend into the apertures in the respective end insulating plates to form a sparkgap with the electrode abutments also positioned in said apertures.
 15. A sparkgap assembly as defined in claim 14 wherein said holding means comprises means defining at least two spaced-apart apertures in each of said terminal plates, and cooperating abutments on the outer surfaces of the end insulating plate members that fit snugly into said apertures to restrict movement between the terminal plates and the insulating plate members, and including a plurality of abutments on said terminal plates the outermost protruding surfaces of which lie in a common plane with the outermost surfaces of the abutments on said insulating plate members when said terminal plates are mounted in operative position in said sparkgap assembly.
 16. A sparkgap assembly comprising a plurality of stacked insulating plate members, means defining an aperture through each of said plate members, a number of elongated electrodes, each of said electrodes comprising a generally flat body portion and a pair of integral abutments protruding respectively from opposite sides of said body portion, means supporting each of said electrodes in relatively fixed position between a pair of said plate members with each of the abutments of the electrodes extending partially into one of said apertures, a pair of terminal plate means respectively mounted over the outermost ends of said stacked insulating plate members, each of said terminal plate means comprising three electrically conductive leg portions that are mounted in generally parallel relationship to each other, and means electrically connecting said three leg portions together adjacent one of the mutually juxtaposed ends thereof, said legs being spaced apart sufficiently to prevent arcs from being formed between them when the sparkgap assembly is operative to discharge an overvoltage surge between said terminal plates, holding means for holding each of said terminal plates in relatively fixed position with respect to the apertures through the end insulating plate members thereby to form a sparkgap between each of the middle legs of the terminal plate means and the respective electrode abutments extending into the apertures in said end insulating plate members. 